Exposure process is one of important fabrication processes in manufacturing a semiconductor device, and in the exposure process, a pattern on a mask plate is accurately transferred onto a photoresist by photochemical reaction. For example, in a manufacturing process of an array substrate (comprising thin film transistors (TFTs)) of a display device, a corresponding material film layer (e.g., an indium tin oxide layer, or the like) is firstly coated or sputtered on a base substrate, a photoresist is then coated on the material film layer, a fine pattern on a mask plate is transferred to the photoresist by performing processes such as exposure, development and the like on the photoresist, and subsequently, the material film layer is etched under the protection of the photoresist, so as to finally form a pattern of a corresponding layer in the array substrate.
Photo mask is an important medium used in the exposure process, FIG. 1 illustrates a patterning structure in an existing photo mask for forming a rectilinear pattern, and the patterning structure is strip-like. In the exposure process, the patterning structure on the photo mask is analyzed and copied onto a patterning layer by an exposure machine. The resolution R of the exposure machine can be calculated according to the Rayleigh's equations:R=K1*λ/NADOF=K2*λ/(NA)2 
where R is the resolution; K1 is a process factor and may be a fixed value in the range of 0.6 to 0.8; λ is the wavelength of exposure light; NA (numerical aperture) indicates ability of collecting diffracted light, and is one of characteristic optical parameters of the exposure machine;
DOF refers to depth of focus. The focus is a point at which the image is presented best, the depth of focus is a range near the focus, and the image continuously remains clear in the range of the depth of focus; K2 is a process factor.
It can be seen that the solution R decreases as the value of NA increases (the smaller the resolution R, the higher the resolving power of the exposure machine), and the depth of focus decreases rapidly as the value of NA increases. It can be known from the Rayleigh's equations that, a higher resolving power is achieved at the expense of the depth of focus, however, the smaller the depth of focus, the smaller the margin of the process, and the higher the process requirement, and thus, a better control means of the depth of focus is required for a device.
In an existing exposure process, due to the limitation of the resolving power of the exposure machine, degree of distortion of an image formed after being exposed by the exposure machine increases when a line width of a micro-pattern reaches or exceeds the resolving power of the exposure machine (i.e., the line width of the micro-pattern is equal to or even smaller than the resolution R), which deteriorates uniformity and profile of the line width, further results in a defective exposure process, and degrades quality of a semiconductor device.